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1!Today’s topics:! Characterizing geologic time! Relative ages (stratigraphy)! Absolute ages (radioactive decay)!Today’s topics:! Earth History! Mass Extinctions! Geologic Time Scale!Class updates:! Reading: Section 4.0-4.6! Homework 1 due today! Homework 2 online, due next Mon.! Midterm practice online (website)! Midterm review online (website)! Midterm 1 on Feb. 28th (next Mon.)!How old is that rock? !2!Determining Relative Geologic Time!1. Principle of Original Horizontality!2. Principle of Superposition!3. Principle of Cross-Cutting Relationship!4. Principle of Faunal Succession!Principle of Original Horizontality!Principle of Original Horizontality!3!Principle of Superposition!Principle of Superposition!Principle of Cross-Cutting Relationships!4!Principle of Cross-Cutting Relationships!Principle of Cross-Cutting Relationships!Order of Events?!5!Grand Canyon"Example!Order of Events?!Principle of Faunal (fossil) Succession!Index Fossils! Def.: accurately indicate the ages of sedimentary rocks!! 1) Abundantly preserved in rocks!! 2) Geographically widespread!! 3) Fast evolving - existed for a relatively short time!! 4) Easily identified!6!Relative Dating: Unconformities!The Great Unconformity!Types of Unconformity!7!Types of Unconformity!Types of Unconformity!Relative Dating: Correlation!8!How old is that rock? ! Relative age: order of events! Absolute age: age in years!Relative dating tells us what order things happened, but not how many years ago they happened.!Absolute Dating: Radioactive Decay!Radioactive Half-Life!9!Half-life Example!• You start with $1000 in your bank account!• Every week your spouse or boyfriend/girlfriend removes half of the money!• The half-life of your account = 1 week!1 week!Your Bank Account!• Start: $1000!• Week 1: $500 !• Week 2: $250!• Week 3: $125!• Week 4: $62.50!• Week 5: $31.25!• Week 6: $15.63!• Week 7: $7.81!• Week 8: $3.90!• Week 9: $1.95!• Week 10: $0.98!• Week 11: $0.49!• Week 12: $0.24!• Week 13: $0.12!• Week 14: $0.06!• Week 15: $0.03!• Week: 16: $0.015 left in your bank account!(1 half-life)!Isotopes & Half Lives!Young things!Old things!10!Radiometric Dating!Radioactive Decay Curve!Calculating Absolute Age!• Potassium-40 included in mineral (start clock)!• Begins decaying to Argon-40!• Brilliant scientists have told us the half-life of K-Ar is ! ! 1.3 billion yrs (Gyr)!• We count # parents & daughters in sample!• We find that our sample contains 50% K & 50% Ar!• So 1/2 of our initial sample (K) has decayed!• How old is it?!• We find another sample that is 25% K & 75% Ar!• How old is it?!11!Mass Extinctions!A Bad Day…. 65 Million Years Ago!12!! Mass Extinctions:!Extraterrestrial Impacts!Fig. 4-2, p.75 Mass Extinctions:!Volcanic Eruptions!Fig. 4-2, p.75 Example Eruptions: !13!Mass Extinctions:!Atmosphere-Ocean-Continent Interactions!Evolution of Earth Atmosphere!Nitrogen!Oxygen!All Others!Fig. 4-2, p.75 Mass Extinctions:!Atmosphere-Ocean Interaction (1)!14!Mass Extinctions:!Atmosphere-Ocean Interaction (2)!Mass Extinctions:!Atmosphere-Ocean-Continent Interactions!Mass Extinctions:!Ocean-Continent Interaction !15!Geologic Time & Biology!Geologic time (millions of years)!Fig. 4-1b, p.74 Geologic Time & Biology!Geologic time (millions of years)!Geologic Time & Biology!Geologic time (millions of years)!16!Geologic Time! Major divisions! Cenozoic: 66 - 2.5 m.y.a! Mesozoic: 245 - 66 m.y.a.! Paleozoic: 544 - 245 m.y.a.! Precambrian: pre-544 m.y.a.! (proterozoic) !Geologic Time!Precambrian (4.6 Ga – 570 Ma)!17!Paleozoic Era (570 Ma - 245 Ma)!Mesozoic Era"(245 Ma – 66 Ma)!Cenozoic Era (66 Ma - present)!18!• Satellites! ! ! 1 (Moon)! !!!• Size (radius)! ! ! 6378 km! !• Bulk density! ! ! 5.5 g/cm3 (4.1 g/cm3uncompressed)!• Surface gravity ! ! 9.8 m/s2!• Tectonism, volcanism!! yes (today)! ! !• Rotation ! ! ! 1 day!• Orbit!! ! ! 365.25 days!• Atmosphere !! ! 78% N2, 21% O2!• Surface pressure! ! 1 atm!• Surface temperature! 20°C (diurnal, seasonal changes)!• Plate tectonics! ! yes!• Water! ! !


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UTEP GEOL 1312 - GEOL 1312 Class 4 Notes

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